1. Field of the Invention
The present invention generally relates to impact instruments including hammering devices such as claw hammers, ball-pein hammers, axes, hachets, sledges, and the like, and also including recreational devices such as croquet rackets, badmitten racquets, tennis racquets, racquetball racquets, golf clubs, baseball bats, softball bats, cricket bats, hockey sticks, and the like. An embodiment of the invention relates to an impact instrument having an improved mass distribution. Another embodiment relates to an impact instrument that includes a handle that focuses the contact of the hand onto a more limited region. Another embodiment relates to an impact instrument that includes a pivoting handle. Yet another embodiment relates to an impact instrument having a handle that dampens and/or decrease shock and vibration. These embodiments may be used independently or in combination to increase the peak impulse produced by the impact instrument and/or to decrease or dampen shock/vibrational forces felt by a user of the instrument.
2. Description of the Related Art
FIG. 1 illustrates a conventional hammer 10 that includes a head 12 and a shank 14 extending from the head. The head terminates at one end in an impact surface 18 through which the hammer delivers an impulse during use. An actual pivot point 16 exists on the shank about which the hammer is pivoted or rotated in the hand during use. Hammers are typically grasped in a user's hand(s) during use and so pivot point 16 may actually be an extended pivot (i.e., a pivot region) rather than a point pivot, since the hammer pivots about a region of finite width (i.e., a hand). Nevertheless the center of this extended pivot region is generally the pivot point 16. When the hammer is grasped in the hand, pivot point 16 may be approximated to lie at a point along the shaft that is proximate the center of the middle finger of the hand. Obviously the pivot point 16 varies depending on where the hand is grasping the shank 14.
The center of impact surface 18 is separated from pivot point 16 by a vertical distance d as illustrated in FIG. 1. The center of percussion is located at a distance b from pivot point 16. The center of percussion is the point at which an impulse could be applied in a direction perpendicular to shank 14, thereby causing shank 14 to pivot about a point, such that there is minimal (in a real world application) or no force (ideally) that is perpendicular to the longitudinal axis of the shank. It should be noted that the center of percussion is not necessarily the same as the center of mass. In most objects the center of percussion is not the same as the center of mass.
The radius of gyration is separated from the actual pivot point by a distance k. The radius of gyration, k, is the distance from the actual pivot point to a location at which the mass of the hammer could be concentrated without altering the rotational inertia of the hammer about the actual pivot point. The locations of the radius of gyration and the center of percussion both depend upon the actual pivot point and the mass distribution of the hammering device. The moment of inertia, I, the radius of gyration, k, and the mass of the hammering device, m, are related by the following equation: I=m·k2. The center of mass of the hammer is located at a vertical distance h from pivot point 16.
The “ideal pivot point” is defined as follows for the purposes of this application. It is believed that distance b will always be equal to k2 divided by h (i.e., k2/h). Thus the “ideal pivot point” is when b, as calculated by the equation b=k2/h, is equal to d. Stated another way, for an impact instrument the ideal pivot point is the pivot point where the center of percussion coincides with the center of the impact surface. In most cases, the “ideal pivot point” 20 exists at a location (e.g., on an elongated member) where an impulse could be applied in a direction perpendicular to the elongated member, thereby causing the elongated member to pivot about a point, such that there is no reactive force that is perpendicular to the longitudinal axis of the elongated member at that point.
Conventional impact instruments (e.g., hammers) tend to have an ideal pivot point that does not coincide with pivot point 16 when held by the typical user. That is, during normal use the center of percussion does not typically coincide with the center of the impact surface of a conventional impact instrument (e.g., hammer), which tends to make use of the impact instrument (e.g., hammer) inefficient and uncomfortable. The amount of vibration felt by the user tends to increase as the vertical distance between the actual pivot point and the ideal pivot point increases. In most conventional hammers, for instance, the ideal pivot point is often displaced from the actual pivot point in a direction toward head 12. For hammers that weigh about 1–2 pounds, the ideal pivot point is frequently between about 0.3 cm and about 3.0 cm removed from the actual pivot point.
During use of a hammering device, it is generally desirable to grasp the hammer at a location such that at least a portion of the hand is proximate or at least in the vicinity of the end 17 of the hammer as shown in FIG. 1. Grasping the hammer proximate the end allows the user to impart a given impulse to a target object with relatively less effort than if the hammer is grasped at a location that is higher up on the shank in a direction towards the head. If the hammer were grasped at the ideal pivot point of a conventional hammer, the “moment length” between the hand and the impact surface would be shortened, tending to result in more inefficient use of the hammer.
It is desirable that an improved impact instrument be derived to deliver a greater impulse and reduce vibration and shock imparted to the user of the device.
U.S. Pat. No. 4,870,868 relates to a sensing device that produces a response when the point of impact between an object and a member occurs at a preselected location on the member.
U.S. Pat. No. 5,289,742 to Vaughan relates to a shock-absorbing device for a claw hammer to dampen vibrations occurring through a steel hammer head.
U.S. Pat. No. 5,375,487 to Zimmerman relates to a maul assembly having a maul head with an annular body that is partially filled with a quantity of flowable inertia material.
U.S. Pat. No. 5,259,274 to Hreha relates to an internally reinforced jacketed handle for a hand tool.
U.S. Pat. No. 5,362,046 to Sims relates to vibration damping devices placed in the butt end of implements which are subject to impact.
The above-mentioned patents are incorporated herein by reference.